Man i procrastinated on a drek skeleton for... 5 years! Long but yeah! Here is a skeleton.

First we can start with the skull... Shape varies! drekir have a lot of headshapes so some drekir have just straight up larger skulls than others! pretty straightforward.

Their torso is very dense and their organs are also packed pretty tight in there under an extended rib cage and a very extended sternum with an extended collar on the back. The sternum and collar extending across the belly and back broadly stop a drek from actually being able to bend their torso much as they only really stop at the hip and even then a drek just doesn't have the muscles to bend much at all. A dreks torso is like an iron pipe, its not built to bend. Drekir can rotate their hips relative to their torso though! And it's common for drekir to rotate their hips to the side while laying down, basking, etc. I've drawn that specific sort of pose maaaany times! But its mostly a flexibility reserved for the back half of a dreks body, the legs, pelvis, and boot.
This overall lack of biomechanical ability to bend the torso is mostly a sivilão related matter. Drekir were made to be pack mules and having an inflexible back helps in supporting a lot of heavy weight related to their jobs. The ability to somewhat pivot their hips is mostly unintentional but helps a lot in sunbasking and general laying about so it never really got stamped out by the sivilão.

Drek arms are nothing really crazy or special, if anything they are rather human like! They do the job! They are small boned which does limit how much muscle a drek can realistically build up on their arms. As such drekir will never have the sheer arm strength of a human. But they weren't built to have strong versatile arms, they were built to pull things and occasionally use their arms to attach packs to their denmates for the labor of the sivilão!

Drek leg bones are more similar to a horses bones than anything, complete with an incredibly dense metacarpal and phalanx bone set! Drek legbones are very dense to withstand the fact a drek both is gonna be really using and abusing their legs over decades of life and that a broken leg bone means a completely crippled drek. So a very thick bone that's resistant to the stresses of daily intense use is important!

The leg muscles of a drek are what gives power to their stalwart, inflexible backs and their thick leg bones, supporting strong muscles (with the boot) are what gives those legs that strength. I would argue a dreks leg muscle group is notably larger than any human muscle. A punch from a drek may not be that crazy... a kick from a drek would probably collapse a rib cage if done at full force.

A dreks pelvis and hip are pretty theropod like as they have a very pronounced boot which, in this case, is for their leg muscles, tail muscles, and some of their back muscles. The pubic boot is perhaps the largest bone a drek actually has in fact! as it has some of a dreks largest muscles fixed to it. So for those who have asked me for years why drekir have a big bump in the rump its actually just a hip bone!

And lastly the spine is... a spine! Nothing special!